1. Field of the Invention
The present invention relates to a fuel cell stack including a stack body formed by stacking a plurality of unit cells in a stacking direction and a box-shaped casing containing the stack body. Each of the unit cells includes an electrolyte electrode assembly and separators sandwiching the electrolyte electrode assembly. The electrolyte electrode assembly includes a pair of electrodes and an electrolyte interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs an electrolyte membrane (electrolyte) comprising a polymer ion exchange membrane. The electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly. The membrane electrode assembly is sandwiched between separators to form a fuel cell.
In use, normally, a predetermined number of (e.g., several tens to several hundreds of) fuel cells are stacked together to form a fuel cell stack to obtain the desired electrical energy. In the fuel cell stack, in order to prevent the increase of the internal resistance in the fuel cells, and degradation of performance of preventing leakage of reactant gases, it is necessary to reliably apply pressures to each of the stacked fuel cells.
In this regard, for example, a fuel cell stack disclosed in Japanese Laid-Open Patent Publication No. 2002-298901 is known. In the fuel cell stack, a stack body is formed by stacking a predetermined number of unit cells, and current collecting terminals (terminal plates) are provided outside the stack body, and end plates are provided outside the current collecting terminals. The end plates are coupled to a casing by a hinge mechanism. The casing includes a plurality of panels provided on upper and lower, and left and right sides between the end plates.
In the structure, the number of components is reduced effectively, and it is possible to use thin end plates. As a result, reduction in the overall size and weight of the fuel cell stack is achieved easily.
In the conventional technique, as shown in FIG. 6, the end plate 2 of the casing 1 is fixed to four side plates 4a, 4b, 4c, and 4d by a hinge mechanism 3. The hinge mechanism 3 includes tabs 5 provided on four sides of the end plates 2, and tabs 6 of the side plates 4a to 4d. The tabs 5 and the tabs 6 are provided alternately. In this state, coupling pins 7 are inserted in these tabs 5, 6.
In the casing 1, a power generation surface 8 is provided, and passages 9a to 9f for supplying an oxygen-containing gas, a fuel gas, and a coolant in a stacking direction are provided on both sides of the power generation surface 8.
In the structure, at the time of assembling the fuel cell stack by placing the unit cells in the casing 1, the desired tightening load is applied to the components between the end plates 2 of the casing 1. Thus, in the hinge mechanism 3, the load applied to the members at the center in the axial direction of the coupling pin 7 is larger than the load applied to the opposite ends in the axial direction.
However, in particular, the coupling pin 7 connecting the end plate 2 and the wide side plates 4b, 4d is significantly long. Therefore, large deformation of the coupling pin 7 may occur easily. Under the circumstances, it is not possible to apply the desired electrode load over the entire power generation surface 8 suitably. Further, a relatively large stress is generated in the hinge mechanism 3 easily, and the strength of the hinge mechanism 3 may be decreased undesirably.